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TRW/Ball/Kodak Competition Sensitive

TRW

James Webb Space Telescope (JWST) Architecture and Overview

Don Davies JWST Town Meeting 7 January 2003

This briefing package is approved for public release."

TRW/Ball/Kodak Competition Sensitive

JWST Observatory Architecture

Optical Telescope Element (OTE) · Stable over total field-of-regard · Beryllium (Be) or ULE optics · Performance verified on the ground · Simple and low risk · Four deployments Primary Mirror (PM) ­ 7 meter · 36 (1 m) hex segments simplify mfg and design · Simple semi-rigid WFS&C for phasing · Tip, tilt, piston, and radius corrections · Segment performance demonstrated · Deployable chord fold for thermal uniformity · Stable GFRP/Boron structure over temperature ISIM · 3 SIs and FGS · Large volume · Simple three-point interface Sunshield · Passive cooling of OTE to <40K · Provides large FOR · Limits momentum buildup Tower · Isolates telescope from spacecraft dynamic noise

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Secondary Mirror (SM) · Deployable tripod for stiffness · 6 DOF to assure telescope alignment

Spacecraft Bus · Isolates reaction wheel noise · Heritage components

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Observatory Design Requirements

Requirement Value Estimated Performance 29.4 m2 82% 0.31% worst case over FOR Comply (details in later chart) 100% 48.9% >55% of sky for >194 days Comply 77.2% (92% OTE&SC/85% ISIM) 105 square arc-minutes ­ can be larger Comply; ~509 kg reserve over and above contingency

Aperture >25 m2 collecting area Encircled Energy >75% for 150 mas radius at 1 µm PSF Stability <2% RMS variation about mean over 24 hours at 150 mas radius at 1 µm Sensitivity Minimum target sensitivities at 4 wavelengths Field of Regard 100% of celestial sphere over one year (FOR) >35% at any time >50% of sky for >60 days Continuous within 5° of Ecliptic pole Observatory >70% Efficiency (85% OTE and Spacecraft/85% ISIM) Instrument FOVs Spatially separated FOVs, SI + FGS FOV > 68 square arc-minutes Launch Mass <5400 kg (includes 1400 kg GFE ISIM)

Performance and design margins are ample to ensure Performance and design margins are ample to ensure meeting science needs as the design is matured. meeting science needs as the design is matured.

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Observatory Sensitivity

· SNR = 10; 100,000 second integration; point target at North ecliptic pole · End-of-life conditions, worst-case scattering · ISIM performance from Appendix A of Level 2 Specification

Sensitivity for Science Observations (nJy) 105

Sensitivity Predictions (29.4 m2 area) Using JWST Mission Simulator

Level 2 Requirement

MIRI, R = 1500

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Margin on required sensitivity ~20% to 59%

NIR, R = 1000 10

MIRI, R = 3

NIR, R = 5 0.1 NMS 3.1 0.1 1 Wavelength (µm) 10 100

Elapsed time for design reference mission (DRM) predicted Elapsed time for design reference mission (DRM) predicted to be 2.54 years versus 2.5-year goal / /5-year requirement. to be 2.54 years versus 2.5-year goal 5-year requirement.

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Pre-Commissioning Activities Before Achieving L2 Orbit

Main Engine Start 1 Main Engine 264 sec Cut-Off 1 785 sec

Launch

~1,500,000 km

L2 orbit achieved L + 109 days

Initiate ISIM testing and certification L + 113 days

Trajectory correction maneuver 1 L + 15 hrs Sunshield deployment L + 2 days Main Engine Start 2 1694 sec Main Engine Cut-Off 2 2084 sec

JWST separation 39 min

L2

~374,000 km ~1,500,000 km

Telescope deployment L + 4 days

Observatory available for ISIM activities L + 70 days Observatory first light (ISIM at safe operating temp) L + 59 days

Trajectory correction maneuver 2 (if required) L + 25 days

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PM Semi-Rigid Hexagonal Segments is a Key Enabler of the Observatory Optical Performance

Simplifies WFS&C (144 actuators) Simplifies WFS&C (144 actuators) · Tip, tilt, piston, and ROC control · Tip, tilt, piston, and ROC control piston · Rigid body motion is independent of · Rigid body motion is independent of radius of curvature control radius of curvature control · Rigid body corrections do not induce · Rigid body corrections do not induce surface distortions or stress surface distortions or stress

Radius of Curvature Actuator Strongback

· Observatory optical quality (mid and high spatial frequency) is manufactured into segments · Segments fully tested before OTE assembly

Strongback

· Fabrication and performance demonstrated for baseline Be material · Mirror architecture can use Be or ULE both these AMSD developers are on the team · Efficiency in production - same physical structure · Simplifies system optic performance endto-end test at temperature prior to launch

Load Spreader

Load Spreader

Radius of Tip/Tilt/Piston Actuators Curvature Actuator

Final selection of mirror material will be made using AMSD results. Final selection of mirror material will be made using AMSD results.

Tip / Tilt / Piston Actuators

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Design Residual WFE Provides a Large FOV for Accommodating ISIM FPA Layouts

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Field Position (arc-minutes)

20

30 25

0

MIRI 2' x 2'

NIRCam

­2

FGS A 4.1' x 2.05'

14 FGS B 10 4.1' x 2.05' 7 5 5

NIRSpec 3' x 3'

· WFE Budget assumes 13nm for Design Residual

7 10

­4

14

­6 ­6 ­4

WFE contours (nm rms)

­2 0 2 4

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Population of FOV needs to be addressed relative to Population of FOV needs to be addressed relative to performance, packaging and spare FGS operations performance, packaging and spare FGS operations

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